Variable resistors and potentiometers



y 7, 1959 J. H. BURDEN 2,894,238

VARIABLE RESISTORS AND POTENTIOMETERS Filed Jan. 24, 1958 United States Patent r 2,894,238 YA'RIABLE RESISTORS AND POTENTIOMETERS James Henry Burden,Swindon, England, assignor to The Plessey Company Limited, llford, England, a British company Application January 24, 1958, Serial No. 711,101

Claims priority, application Great Britain February 25, 1957 4 Claims. (Cl. 338-174) This invention relates to variable resistors and potentiometers and constitutes an improvement in or modification of the invention described in our co-pending British application No. 4,826/ 56 (U.S.A. Serial No. 655,456, now Patent No. 2,863,030; French No. 73/456 and German P 17 957) hereinafter referred to as the main patent. In the complete specification of the main patent we have described and claimed a variable resistor or potentiometer, which will hereinafter be referred to as a resistor device of the kind specified, wherein the electrically operative elements are combined in a self-contained sub-assembly ready for the insertion of an actuating spindle. In the specific embodiment described and illustrated in the said complete specification, this sub-assembly includes a stop in the rotary part of the sub-assembly, adapted to cooperate with a fixed abutment in a housing or the like in which the sub-assembly is to be fitted. This construction involves certain stresses of the insulating material of which the body of the rotary part of the sub-assembly is normally constructed, at the moment at which the stop strikes the fixed abutment, and it is an object of the present invention to provide an improved construction in which the mechanical stress due to the limitation of rotary move ment is kept away from the rotary body of the subassembly.

According to the present invention the actuating spindle of a resistor device of the kind specified is provided with a stop member participating in the rotation of the spindle and co-operating with a fixed abutment provided on a housing member incorporating the bearing for the actuating spindle. Preferably the stop member forms part of a body which serves to limit the axial movement of the spindle relative to the bearing by co-operating with the inner end of the bearing bush or the like, while axial movement in the opposite direction is preferably prevented by a circlip or other suitable abutment at the outer end of the bearing bush.

The invention is illustrated in the accompanying drawing, which is generally similar to Figure 3 of the drawing of the main patent.

In this accompanying drawing parts which are substantia'lly identical with the corresponding parts of the main patent have been marked by the same reference numerals as in the specification of the main patent.

Referring now to the drawing- A base or stator element 1 made of insulating material, for example of a phenolformaldehyde plastic, carries on one of its faces a part-annular resistance track 2 and, concentric therewith, a contact ring 3, both accommodated in suitable groove-like recesses. A movable contact element for co-operation with the track 2 and contact ring 3 is constituted by a resilient contact carrier 4, which is equipped with contact brushes 5 and 6 respectively engaging the tracks 2 and 3. A hub member or bush 7 extending through and guided in a central cylindrical aperture 8 of the base 1 is provided with a flange 9 which faces the tracks 2 and 3 in spaced relation. The contact carrier 4 is located relative to the bush 7, so as to maintain the brushes 5 and 6 in respective engagement with the tracks 2 and 3, by an eccentric portion 19 of the bush and by being formed at diametrically opposite points with deflected coupling lugs which engage corresponding recesses of the flange 9, thus coupling the contact carrier with the hub for common rotation; the curved back of the contact carrier is supported against the flange 9, so that its resilience in conjunction with the spacing between this flange and the base 1 determines the contact pressure by which the brushes 5 and 6 are applied to the tracks 2 and 3. This spacing is determined by a stop in the form of a washer 12 of resilient metal provided with internally projecting tongues 13 which are deflected or, since preferably a Washer having pre-bent teeth is employed, further deflected as the washer is forced onto the bush 7. This sliding-on movement is limited by the abut ment of the end face 20 of eccentric bush portion 19 against the face of the base 1 or contact ring 3. A plain metal washer 14 is preferably interposed between the washer 12 and the back of the base 1. The bush 7 has a serrated through bore 18a engaged by a fluted portion 25a of an operating shaft 24. This shaft is journalled in the mounting brush 26a of a housing base 37, but while in the main patent axial movement of the actuating spindle 24 is prevented by two circlips 28 engaging corresponding grooves of the spindle 24, the inner circlip is replaced in the illustrated improved or modified construction by a substantially disc-shaped member 41, preferably formed with a narrow upturned rim 43, a part of which is extended to form a stop lug 42. The housing base 37, which take the place of the housing base 27 of the main patent, is formed at a suitable point of its wall portion with an inwardly projecting abutment 40 formed by depression of the wall material with a suitable punching tool; this abutment projects into the path of the stop member 42 and thereby limits rotation of the shaft 24. In View of its relatively great radial thickness the disc member 41, instead of engaging a groove on the shaft in circlip fashion, is pressed on to the fluted end portion 25a of the shaft 24. For this reason this fluted portion 25a is correspondingly extended in the axial direction as compared with the fluted portion 25 shown in the main patent.

Since the construction of the present invention limits the rotation of the shaft, the provision of the stop 16 of the main patent in the rotary insulating body 9 becomes unnecessary, and as a result it has been possible to reduce greatly the axial length of the corresponding body 9a in the illustrated embodiment, and the axial length of the cap 31b could, for the same reason, be likewise reduced compared with the cap 31 of the main patent, thereby achieving a reduction in the overall length of the device. Apart from the modifications herein described the device operates in the manner described with reference to Figures 1 to 3 of the main patent.

What is claimed is:

1. A rotary type variable resistor device comprising a support member having a journal bearing, a self-contained variable-resistor unit including a stator equipped with a resistor track and having a central bore, a rotor body of insulating material having a boss extending through and journalled in said central bore of the stator, a wiper member mounted for rotation with the rotor relative to the stator and co-operating with the resistor track, and means for axially locating the rotor relative to the stator, said boss having a longitudinal bore of non-circular cross-section, means for securing the stator on the support member, a shaft rotatably mounted in the journal bearing of the support member and projecting therefrom at both ends of said bearing, one end of said shaft having a non-circular cross-section which with a sliding fit engages the bore of the rotor, a stop member mounted with an interference fit on the non-circular portion of the shaft between the bearingand the rotor for rotation with the shaft, and locating means holding the shaft against axial displacement, the support member being provided with an abutment co=operating with the stop memberto limit the rotation of the shaft in the bearing.

2. A variable resistor device as claimed in claim 1, wherein the stop member is arranged in contact with the surface of the support member at one end of the bearing to prevent axial movement of the shaft in one direction.

3. A device as claimed in claim 2, including a circlip located in a groove at the opposite end of the bearing to prevent axial movement of the shaft in the opposite direction to that prevented by the stop member.

4. A variable resistor device as claimed in claim 1, including a housing member placed over the stator member to cover the ends of the shaft and the resistor track, said housing member being provided with prongs and said support and stator member being provided with recesses, said prongs co-operating with said recesses for holdingsaid housing member in position and securing the stator to the support member and preventing rotation of the stator relative to the support member.

References Cited in the file of this patent UNITED STATES PATENTS 2,789,191 Arisman' et al Apr. 16, 1957 

